Automatic transmissions, especially for motor vehicles, include planetary gear sets according to the state of the art, which are shifted using friction or shifting elements such as couplings and brakes; are usually connected with a starting element subject to a slip effect and are optionally provided with a bypass clutch, such as a hydrodynamic torque converter or a hydraulic coupling.
A transmission of this type is revealed in EP 0 434 525 A1. It basically includes an input shaft and an output shaft, which are arranged parallel to each other, double planetary gear sets arranged concentrically in relation to the output shaft and five shifting elements in the form of three clutches and two brakes, whose selective locking respectively determines in pairs the different gear reductions between the input shaft and the output shaft. Hereby, the transmission has a front-mounted gear set and two power paths so that six forward gears can be attained through the selective engagement in pairs of the five shifting elements.
Two clutches are needed, in connection with the first power path to transmit the torque from the front-mounted gear set to two elements of the double planetary gear set. These are basically arranged behind the front-mounted gear set in the direction of the double planetary gear set in the direction of the power flow. A further clutch is provided, in connection with the second power path, which detachably connects this with a further element of the double planetary gear set. The clutches are arranged in such a way that the internal disk support forms the output.
Furthermore, a compact multi-step transmission in planetary construction, especially for a motor vehicle, is known from the publication U.S. Pat. No. 6,139,463, which has two planetary gear sets and one front-mounted gear set, as well as three clutches and two brakes. Two clutches C-1 and C-3 are provided with this known multi-step transmission in connection with a first power path for transmitting the torque from the front-mounted gear set to the two planetary gear sets. The external disk support or the cylinder or the piston or the pressure compensation side of clutch C-3, is connected with a first brake B-1. Moreover, the internal disk support of the third clutch C-3 is connected with the cylinder, or piston or pressure compensation side of the first clutch C-1, whereby the internal disk support of the first clutch C-1 is arranged on the output side, and is connected with a sun wheel of the third planetary gear set.
Additionally, a multi-step transmission is known from DE 199 49 507 A1 of the Applicant, in which two non-shiftable, front-mounted gear sets are provided on the input shaft, which generate two speeds on the output side that can, in addition to the speed of the input shaft, be shifted selectively to shiftable double planetary gear sets acting on the output shaft through the selective closing of the shifting elements in such a way, that in each case only one shifting element of the two shifting elements just activated must be engaged or disengaged for shifting from one gear into the respectively next following higher or lower gear.
Furthermore, an automatically shiftable, motor vehicle transmission with three spider supported planetary gear sets, as well as three brakes and two clutches for shifting six forward gears and one reverse gear, and with an input shaft, as well as an output shaft, is known from DE 199 12 480 A1. The automatically shiftable motor vehicle transmission is constructed in such a way that the input shaft is directly connected with the sun wheel of the second planetary gear set, and that the input shaft can be connected with the sun wheel of the first planetary gears through the first clutch, and/or through the second clutch with the planet carrier of the first planetary gear set. In addition or as an alternative, the sun wheel of the first planetary gear set can be connected through the first brake with the housing of the transmission and/or the planet carrier of the first planetary gear set through the second brake with the housing and/or the sun wheel of the third planetary gear set through the third brake with the housing.
The present invention is based upon the objective of proposing a multi-step transmission of the type stated above, in which the construction effort is optimized and, moreover, the degree of efficiency in the main driving gears is improved with respect to drag and gearing losses. Additionally, low torques are supposed to act on the shifting elements and planetary gear sets in the multi-step transmission of the invention, and the speeds of the shafts, shifting elements, and planetary gear sets are supposed to be kept as low as possible. Furthermore, the number of gears, as well as the transmission ratio spread are supposed to be increased.